Stress urinary incontinence (SUI) is the involuntary urine leakage on effort or exertion and is the most common form of urinary incontinence. SUI is a common condition, particularly among women, affecting about 35% of women over the age of 40, and is strongly correlated with vaginal delivery, which can injure the nerve, muscle, and collagenous tissues responsible for maintaining continence. The only rehabilitation method for the maternal injuries of childbirth is pelvic floor (Kegel) exercises which strengthen the muscles of the pelvic floor and prevent leakage between voids. However, one half of patients do not achieve success with pelvic floor exercises. Therefore an adjuvant treatment to Kegel rehabilitative exercises is needed. Stem cells participate in normal repair processes and therefore have the potential to be harnessed to facilitate repair of childbirth and other injuries. Cytokine gradients produced by the injured tissues attract or home circulating stem cells to sites of injury, where they facilitate the repair process, sometimes via the same receptor-mediated mechanisms involved in homing. Recent research has demonstrated that the mechanism by which stem cells facilitate repair after injury is by secreting paracrine-acting proteins such as growth factors. Vaginal distension (VD) has been used in rodents to simulate the human maternal injuries of childbirth for investigations of the mechanisms of injury and recovery. VD results in a significant decrease in urethral resistance to leakage, taken as evidence of SUI. Stem cell homing cytokines are upregulated after VD, particularly those that attract adult mesenchymal stem cells (MSCs), and infusion of MSCs after VD results in accelerated recovery of SUI. However, the mechanisms of this improved functional repair are not known. The goal of this proposal is to investigate the mechanisms of accelerated recovery by treatment with MSCs after simulated childbirth injury, in preparation for future clinical trials. The Hypothesis to be tested in this project is that adult MSCs facilitate recovery from SUI after simulated childbirth injury via secretion of paracrine factors as are in concentrated conditioned media (CCM), and this therapeutic benefit can be achieved through the systemic delivery of MSCs due to homing of these cells to the urethra & pelvic organs via a cytokine-receptor-mediated mechanism. The hypothesis will be tested with 3 Specific Objectives (SO). The experiments of SO1 are designed to determine the most effective dosage and timing of MSC or CCM delivery to facilitate recovery from VD. The experiments of SO2 are designed to determine the receptor-mediated mechanisms of MSC homing & accelerated functional recovery from VD. The experiments of SO3 are designed to determine the paracrine factor-mediated mechanisms of accelerated functional recovery from VD. Postpartum SUI is highly predictive of SUI years later even if the postpartum SUI resolves initially. Therefore, women with postpartum SUI who are not nursing could be a population of potential primary candidates for an intervention that would both treat their current incontinence and prevent recurrence of incontinence later in life. Systemic cellular therapy could provide treatment to the site where it is needed with few side effects. In addition, noncellular methods are possible, since the paracrine factors secreted by stem cells could potentially be used to accelerate recovery in the absence of cells, as with CCM treatment. This work also has direct application to polytrauma and other multi-factorial traumatic injuries since the maternal injuries of childbirth are similarly diffuse and involve nerves, muscles, connective tissue by a variety of mechanisms including direct trauma, ischemia, stretch, and avulsion. Therefore, results from this study could be used to propose treatment for other diffuse and multi-factorial traumatic injuries, including polytrauma. As a result this work has application to veterans of OIF/OEF as well as to women and could provide a method of improving rehabilitation from these combinatorial injuries for which recovery is difficult.